1. Field of the Invention
The invention relates to a lock up or limited slip differential mechanism for effectively transferring torque to both of a coaxially aligned pair of axles of a wheeled vehicle. More particularly, the invention relates to a compact differential of the type having a planetary gear assembly which includes an electromagnetically operated clutch mechanism that provides a resistance to excessive relative rotation of the axles of the vehicle.
2. Summary of Related Art
A conventional differential gear is arranged in a vehicle drive train to allow, at the time of turning, the outer wheel to rotate faster than the inner wheel while maintaining an equally divided torque distribution to the left and right wheels, thereby securing a smooth turn. The differential is disadvantageous in driving the vehicle under some conditions. For instance, if one wheel is on a low friction surface, such as ice, high torque cannot be transmitted to the other wheel due to the constitution of the differential. To avoid such a disadvantage, there is provided a differential lock up or limiting mechanism which effects a torque transfer to the wheel on the higher friction surface, thus increasing the total available tractive force for propelling the vehicle and thereby improving the mobility and performance thereof.
In applications where compactness is required, such locking and/or limited slip differentials may include a compound planetary gear assembly, including an annular gear, planetary carrier, planet gears and sun gear, disposed within the differential gear case. A clutch pack is typically disposed such that, when engaged, the sun gear is clutched to the gear case to retard, or even prevent, rotation between the gear case and the sun gear.
Additionally, some sort of actuating mechanism is provided to actuate or move the clutch pack from its disengaged position to an engaged position. Some differentials include an externally controllable clutch mechanism which may vary the amount of clutch force applied independently of the relative rotational speed of the axles. Such mechanisms have been incorporated in a planetary differential, including electromagnet actuation.
In some applications, however, even the current planetary gear type differentials are considered disadvantageously large due in part to the size of the clutch pack and magnet required to achieve the necessary torque transfer capability. The transfer of equal or greater torques is thus required from a more compact assembly than was heretofore possible.